Ionograph tape



April 13, 1943.- 7 E. J. KOHN 2,316,340

IONOGRAPH TAPE Filed )iov/ZS, 1940 EarZJKo/zn INVENJZW ATTORNEY v the tape was treated.

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Patented Apr. 13, 1943 IONOGRAPH TAPE Earl J. Kohn, Columbus, 01110, assignor to El. du Pont de Nemours & Company, Wilmington, Dcl., a corporation of Delaware Application November 23, 1940, Serial No. 366,862

14 Claims.

This invention relates to electrochemical recording, especially the production, on thin, transparent sheet material, of colored tracks corresponding in intensity to variations in electrical current. More particularly, it appertains to regenerated cellulose tapes impregnated with rubianic acid.

In U. S. A. Patent No. 2,038,486 there is a description of a process for the electrochemical recording of electric currents. In this process a record tape (ribbon, web, film) is soaked with a solution comprising essentially the diamide of thio-oxallc acid, the wet tape passed under a copper pin serving as the anode in an electrical circuit which is closed through the solution with which the tape is impregnated, and a black deposit of the copper salt of the'diamide of thiooxalic acid produced on the tape by the passage of an electric current therethrough.

This process has not been found to be practical when the recording tape is made of regenerated cellulose for the reasons inter alia that the trans parency of the tape is adversely affected by the deposit of the dlamide of thio-oxalic acid on its surface, and that the regenerated cellulose tape exhibits its well known tendency to distort by wrinkling and puckering upon drying. As a result of the obscuring by the diamide of thiooxalic acid and the distortion accompanying the distortion of the regenerated cellulose tape of the recorded track, satisfactory reproduction from the record cannot be obtained.

This invention had for an object the production of a regenerated cellulose recording tape which would not have the record track obscured by the electrically responsive composition with which Other objects were to provide a regenerated cellulose recording tape of high transparency and of high rubianic acid content, and to impregnate the regenerated cellu lose with rubianic acid in such a manner that it would not adversely affect the transparency thereof, especially when used for electrochemical recording without introductory moistening with A general advance in the art, and other objects which will appear hereinafter, are also contemplated.

It has now been found that a transparent regenerated cellulose sheet impregnated with a concentration of rubianic acid high enough to enable the sheet to be used for electrochemical recording without being wetted (or moistened) with water (just prior to the recording) can be prepared by impregnating the base sheet material at elevated temperatures with a hot aqueous solution of rubianic acid. Sheet material so produced is free from the surface bloom or blush of rubianic acid which detracts from the appearance of the sheet, impairs the transmission of light through the sheet, and deleter'iously alfects the reproduction from the recorded track (or markings) on the sheet, especially when a photoelectric method of reproduction is utilized.

From the following description and specific examples, in which'are disclosed certain embodiments of the invention as well as details of what is believed to be the best mode for carrying out the invention, it will be apparent how the foregoing objects and related ends are accomplished. The written description is amplified by the accompanying drawing, in which:

Figure 1 is a perspective view showing a record ribbon passing over an electrode roll and under a moistening device and a'stylus, and Figures 2 and 3 are side elevation views of modifications of the device shown in Figure 1. In an embodiment of Figure 1 the electrical circuit wires are connected to the shaft of the electrode roll and the stylus point. The embodiment of Figure 2 is similar, except that the conductor leading to the stylus point extends through the handle of the stylus. In the device of Figure 3, one electrical connection is made to the stylus (as in Figure 1), and the other to the point of the tape moistening device. As a result, the circuit is closed through that portion of the wetted track extending between the points of the stylus and the moistening device.

Parts are given by weight throughout the ap plication, unless otherwise specified.

Example 1 Tapes of gel (material which has been prepared by the process of U. S. A. Patent No. 1,548,864 to'Brandenberger and not yet dried) regenerated cellulose were impregnated by pas sage through an aqueous bath containing 0.5% rubianic acid (the diamide of thio-oxalic acid). The speed of travel was regulated so that each portion of the tape was in the bath for 10 minutes.

The bath was heated by means of a surrounding water bath maintained at 95-97 C. After impregnation the tape was dried by passage over heated rollers of the type disclosed in U. S. A. Patent No. 1,606,824 to Brandenberger. Tapes prepared by this method possessed excellent transparency and appearance and conducted electric current quite readily upon moistening.

Example II Tapes of gel regenerated cellulose were impregnated by passage through an aqueous bath containing 0.3% rubianic acid and 5.0% sodium acetate. The speed of travel was regulated so that each portion of the tape was in the bath for minutes. The bath was heated by means of a surrounding watef bath maintained at 95-97 C. After impregnation, the tape was dried by passage over heated rollers. Tapes prepared by this method possessed excellent transparency and appearance, and conducted electric current quite readily upon moistening.

Example III Tapes of gel regenerated cellulose were impregnated by passage through an aqueous bath containing 0.25% rubianic acid, 8.33% sodium acetate and 13.3% glycerol. The speed of travel was regulated so that each portion of the tape was in the bath for 10 minutes. The bath was heated by means of a surrounding water bath maintained at 95-97 C. After impregnation the tape was dried by passage over heated rollers. Tapes prepared by this method possessed excellent transparency and appearance, and conducted electric current quite readily upon moistening.

Example IV Small sheets of gel regenerated cellulose were placed in an aqueous bath containing 0.25% rubianic acid, 8.33% sodium acetate and 13.3% glycerol for 10 minutes. The bath was maintained at 95-97 C. during the dissolving of the rubianic acid and the impregnation of the sheets. After impregnation, the sheets were blotted and dried on frames in an oven. These sheets, prepared by this method, possessed excellent transparency and appearance, and conducted the electric current quite readily in atmospheres of ordinary (normal) humidity. Voltages of 100 to 150 gave currents on the order of 3 to milliamperes or higher. When a copper anode was used, a black mark was produced upon passage of current where it touched the sheet material.

Example V Viscose was extruded as a web into a coagulating bath regenerated in an acid bath, desulfured, washed, bleached, washed again. and finally passed through an aqueous bath consisting of rubianic acid 0.15%, potassium chloride 1.7%, glycerol 13.3%, and water. The aqueous bath was maintained at a temperature of 95 C. during passage of the web. The web so treated was passed through squeeze rolls which removed excess superficial liquid, and then passed over rolls of a drying apparatus. The web so produced was slit into recording tapes which had excellent transparency and appearance. They were readily marked by the passage of electric current when drawn between contacting copper electrodes at relative humidities of 35% and higher.

Example VI Small sheets of gel regenerated cellulose were impregnated in an aqueous bath containing 0.5% rubianic acid, 2% potassium chloride and 20% triethylene glycol, maintained at a temperature of 95-98 C. After impregnation for 10 minutes, the films were removed, blotted and dried on frames in an oven. The films were then exposed for 16.5 hours to an atmosphere maintained at 7% relative humidity. They were then removed from the air-tight container in which the aforementioned exposure took place, and tested immediately between copper electrodes. Passage of an electric current through the sheet material between the copper electrodes produced marks of a satisfactory intensity and character for the recording of sound.

Example VII Small sheets of gel regenerated cellulose were impregnated by being held for 10 minutes in an aqueous bath containing 1% tannic acid, 1.8% potassium chloride, 13.3% glycerol and 93.9% water. During impregnation the temperature of the solution was maintained at 95-98 C. The sheet material was then blotted and dried on frames in an oven. The finished sheets possessed excellent transparency, and when electric currents were passed therethrough using cast iron and stainless steel electrodes, purplish-black marks excellent for sound reproduction were obtained.

Example VIII Small sheets of gel regenerated cellulose were impregnated in the manner described in Example VII' with an aqueous bath of the composition consisting of 1% tannic acid, 20% triethylene glycol, 1.8% potassium chloride and 77.2% water. The sheets, after being blotted and dried as described in Example VII, were exposed to an atmosphere of 7% relative humidity for 21 hours, and then tested for markings. Very distinct and legible marks were obtained under these conditions (in an atmosphere of 7% relative humidity) when tested with an iron electrode.

As the base sheet, this invention contemplates any smooth, substantially non-porous, non-flbrous sheet, especially cellulosic film precipitated from an aqueous cellulosic or aqueous alkaline cellulosic dispersion or solution. This includes webs of regenerated cellulose, whether precipitated from viscose (solutions of cellulose xanthate), cuprammonium, or any other aqueous solutions or dispersions of cellulose. It also includes sheets of cellulose ethers precipitated from aqueous solutions or dispersions (U. S. A. Patent No. 2,123,883 to Ellsworth), such as glycol cellulose, cellulose glycolic acid, alkyl cellulose (preferably methyl or ethyl cellulose), and the like. These specific cellulose substitution derivatives just mentioned are usually grouped under the generic term low (or lowly) substituted cellulose ethers. In the language of the art, low substituted cellulose derivatives are those in which there is not more than one mol of substitution per glucose unit.

In some of the examples adjuvant materials are employed to improve the conductivity. The chlorides of the alkali metals, especially potassium chloride, sodium chloride and ammonium chloride, are preferred for this purpose. The alkali metal acetates, for example, sodium and potassium acetates, are also very satisfactory. Electrolytes are also very satisfactory and can be satisfactorily applied from the impregnating baths. The alkaline earth halides, particularly calcium chloride, are also suitable for this pur pose. The nitrates and carbonates have not been found very satisfactory, because they effect precipitation of the rubianic acid with the evolution of hydrogen sulfide. Specific examples of such compounds are potassium nitrate, sodium nitrate, ammonium nitrate and potassium carbonate.

In some of the examples a hygroscopic softener (for the regenerated cellulose tape) is also included in the impregnating bath. The last treating bath in the conventional process of preparing regenerated cellulose sheet from viscose, is a softening bath, and it is quite convenient and economical to apply the rubianic acid therefrom. Satisfactory softeners are glycerol, propylene glycol, formamide, triethanol amine, ethylene glycol, diethylene glycol, and triethylene glycol. Numerous other satisfactory softeners are known to the art. and in themterest of brevity are not listed here.

The temperature of the impregnating bath i critical. Although advantages are obtained with impregnating baths with temperatures as low as 85 C., the best results have been obtained when bath (95 C. as a minimum) because rewet sheet has a moisture content of only approximately 100%, whereas gel film obtained by the usual manufacturing processes, contains from 300% to water, based on the cellulose. The replacement of this greater amount of water with impregnating solution gives a higher concentration in the final dry film.

The amount of rubianic acid in the impregnating bath is preferably 0.15% to 0.50%. and in any case should not be much below 0.1%. The upper limit in commercial scale operation is about 1%, but this is not critical. The critical upper limit depends upon the amount of rubianic acid which is precipitated upon the surface of the film. Such a precipitation seriously impairs the transmission of light, which is an important matter when a photoelectric method of reproducing from the markings on the web is utilized. The higher concentrations are more satisfactory so far as response to the electric current is concerned. Proper balance betweenthese advantages and disadvantages can readily be determined empirically, depending upon the specific purpose to which the recording tape is to be put. A range of 0.1% to 1.0% in the impregnating bath corresponds to a range of about 0.3% to 3.0% in the dried film, since drying brings about a concentration of approximately three times the bath concentration. A concentration of rubianic acid in the range 0.45% to 1.5% (based on the weight of the cellulose) in the finished tape, is generally satisfactory and represents the present preferred practice.

The present invention has the advantage oi enabling a high percentage of rubianic acid to cording tape without deleteriously affecting the transparency of the tape, and without obscuring the record on the tape.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. The process of preparing a transparent electrochemical recording sheet material, which comprises immersing regenerated cellulose sheet in an aqueous solution containing 0.1% to 1% rubianic acid, maintaining the solution at a temperature in the range 85 C. to boiling until impregnation has taken place to the extent that the subsequently dried film will contain between 0.3% and 3% rubianic acid, and thereafter removing and drying theimpregnated sheet material.

2. A transparent electrochemical recording tape, comprising a regenerated cellulose ribbon having incorporated therein between 0.3% and 3% rubianic acid to enable the tape to be used for recording without wetting with water preliminary to recording, said tape being free from surface bloom of rubianic acid.

3. A transparent electrochemical recording tape, comprising a regenerated cellulose ribbon having incorporated therein between 0.3% and 3% rubianic acid to enable the tape to be used for recording without Wetting with water preliminary to recording, said tape being free from surface bloom of rubianic acid and containing a hygroscopic softener.

4. The process of preparing a transparent electrochemical recording sheet material which comprises immersing regenerated cellulose sheet in an aqueous solution comprising essentially water, 0.1% to 1% rubianic acid, potassium chloride and hygroscopic softener, maintaining the solution at a vtemperature of 95 C. until impregnation has taken place to the extent that the subsequently dried film will contain between 0.3% and 3% rubianic acid. thereafter removing the impregnated sheet from the solution, and drying it.

5. The process of preparing a transparent electrochemical recording sheet material which comprises immersing regenerated cellulose sheet in an aqueous solution comprising essentially water, rubianic acid 0.5, potassium chloride 2.0% and hygroscopic softener 20%, maintaining the solution at a temperature of 95-98 C. until impregbe incorporated in a regenerated cellulose re- 76 nation has taken place to the extent that the subsequently dried film will contain between 0.3% and 3% rubianic acid, thereafter removing the impregnated sheet from the solution, and drying it.

6. The process of preparing a transparent electrochemical recording sheet material, which comprises immersing regenerated cellulose sheet in an aqueous solution containing 0.1% to 1% rubianic acid, maintaining the solution at a temperature of 95-100 C. until impregnation ha taken place to the extent that the subsequently dried film will contain between 0.3% and 3% rubianic acid, and thereafter removing the impregnated sheet material and drying it.

7. The process of preparing a transparent electrochemical recording sheet material, which comprises immersing regenerated cellulose sheet in an aqueous solution containing 0.1% to 1% rubianic acid and potassium chloride, maintaining the solution at a temperature in the range C. to boiling until impregnation has taken place to the extent that the subsequently dried film will contain between 0.3% and 3% rubianic acid, and thereafter removing the impregnated sheet material and drying it.

8. The process of preparing a transparent electrochemical recording sheet material, which comprises immersing regenerated cellulose sheet in an aqueous solution containing 0.1% to 1% rubianic acid. potassium chloride and hygroscopic softener, maintaining the solution at a temperature in the range 85 C. to boiling until impregnation has iaken place to the extent that the subsequently dried film will contain between 0.3% and 3% rubianic acid, and thereafter removing the impregnated sheet material and drying it.

9 The process of preparinga transparent elec- \rochemical recording sheet material, which comprises immersing regenerated cellulose sheet in an aqueous solution containing 0.15% to 0.50% rubi anic acid, maintaining the solution at a temperaure in the range 85 C. to boiling until impregnation has taken place to the extent that the subsequently dried film will contain between 0.3% and Z rubianic acid, and thereafter removing the impregnated sheet material and drying it.

10. The process of preparing a transparent electrochemical recording sheet material which comprises immersing regenerated cellulose sheet in an aqueous solution comprising essentially water, rubianic acid 0.15% to 0.5%, potassium chloride not over 2.0% and hygroscopic softener not over 20%, maintaining the solution at a temperature of -98 C. until impregnation is complete, thereafter removing the impregnated sheet from the solution, and drying it.

11. A transparent electrochemical recording tape as defined in claim 3 in which the hygroscopic softener is triethylene glycol.

12. The process of preparing a transparent electrochemical recording sheet as defined in claim 5 in which the hygroscopic softener is triethylene glycol.

13. The process of preparing a transparent electrochemical recording sheet as defined in claim 8 in which the hygroscopic softener is t-riethylene glycol.

14. The process of preparing a transparent electrochemical recording sheet as defined in claim 10 in which the hygroscopic softener is triethylene glycol.

' EARL J. KOHN. 

